This invention relates to surfaces for diminishing the Leidenfrost effect and more particularly to surfaces having multiple length-scale textures including micro- and/or nanoscale texturing to diminish the Leidenfrost effect.
The heat transfer of droplets or sprays impinging on a super-heated dry surface or pool boiling can be categorized into four regimes: single-phase liquid evaporative cooling, nucleate boiling, transition boiling and film boiling. See, Bernadin, J. D., et al. “Mapping of Impact and Heat Transfer Regimes of Water props Impinging on a Polished Surface,” Int. J. Heat Mass Transfer 40 (1997) 247-267. The boundary between nucleate boiling and transition boiling is the point of the highest heat transfer coefficient and is denoted as the critical heat flux (CHF) point. The boundary between transition boiling and film boiling is the point of lowest heat transfer coefficient and is denoted as the Leidenfrost point (LFP). The LFP is characterized by levitation of a droplet above a heated surface, supported by the excess pressure of the vapor generated between the droplet and the solid surface. See, Biance, A. L., et al. “Leidenfrost props,” Phys Fluids 15 (2003) 1632-1637. As power densities continue to increase, the nature of the droplet-surface interaction will fundamentally limit this process. This limitation arises from the Leidenfrost effect, in which thin vapor film formation under the drops prevents surface wetting. Under such circumstances, heat transfer occurs via conduction through the vapor films leading to dry-out, catastrophically high surface temperatures, and failure of the device. This fundamental limitation leads to the classical catastrophic kink instability (for temperatures beyond the critical heat flux temperature) in the heat flux versus temperature curve. As a result, two-phase cooling solutions have to operate at significantly lower heat flux levels. Similar limitations are encountered in quenching and some coating processes.
It is an object of the present invention to overcome these significant limitations by engineering multiple length scale super wetting surfaces including surfaces with micro- and nano-structures that can fundamentally alter droplet-surface interactions to continuously rewet the surface, prevent vapor film formation, and enhance the Leidenfrost temperature.